This invention relates to actuator arms for disc drives, and particularly to actuator arms that are aerodynamic to reduce pressure perturbations within the disc drive.
Conventional actuator arms used in disc drives have rectangular cross-sections. The rectangular shape of conventional actuator arms offers substantial resistance to the laminar flow of air associated with a revolving disc. This resistance sheds vortices downstream from the actuator arm, creating a turbulent air flow and vortices in the form of pressure perturbations. These pressure perturbations act as a force against the disc, causing the disc to vibrate in its resonance modes, increasing non-repeatable run-out. Also, the rectangular shape of the actuator arm causes the boundary layer of the flow to separate from the arm just before and just after the actuator arm. A separated flow is inherently unstable and causes pressure perturbations around the actuator arm. These pressure perturbations cause the actuator arm to resonate at its natural frequency, which severely restricts the ability of the servo control system to position the arm accurately relative to the disc surface. This limits the maximum track density in the media.
In addition, the velocity of the air flow is related to the linear velocity of the disc. The linear velocity of the disc is greater at outer tracks than at inner tracks, so the flow velocity of the air varies radially across the disc. Consequently, the pressure perturbations created by actuator arms are different across the disc radius.
The present invention provides a solution to this and other problems, and offers other advantages over the prior art.
According to one embodiment of the present invention, a disc drive actuator arm is provided to position a head relative to a track on a rotating disc. The actuator arm is an extended arm having a forward edge to engage fluid flow due to rotation of the disc, a rear edge, and a top surface and a bottom surface along which fluid flows. The top and bottom surfaces join the forward and rear edges, and the fluid flow has a boundary layer along the top surface and the bottom surface. The arm has an aerodynamic cross-section so that the boundary layer does not separate at the forward and rear edges.
In preferred embodiments, the forward edge is aerodynamically shaped to minimize pressure increases in front of the arm. In other preferred embodiments, the fluid flow is laminar to prevent shedding vortices.